This specification relates to substance analyzers, and more particularly, to a bulk substance analyzer unit that can determine the compositional elements of bulk materials using one or more neutron sources and one or more radiation detectors.
When an atom absorbs a neutron, it increases in atomic weight, but at that moment, the chemical properties of the atom do not change, thus forming a new isotope of the same element. When a neutron is absorbed, the absorbing atom emits one or more gamma rays, the number and energies of which are unique to that element. The new isotope may be unstable and seek stability by emitting one or more forms of radiation over a period of time, which may also result in the atom changing to a different element. Every radioactive isotope has a characteristic half-life as it decays to a stable state. An element that has absorbed a neutron can be identified by either the absorption gamma rays that it emits or by the decay-radiation it emits. The latter is normally referred to as neutron activation analysis and the former is often called Prompt-Gamma, Neutron Activation Analysis (PGNAA).
Commercial PGNAA analyzers were introduced during the 1970s and 1980s. PGNAA can measure material composition throughout a relatively large volume of material because neutrons penetrate matter to a great depth and the resulting prompt gamma rays are of energies high enough to permit them to escape from a substantial depth within the material. When the bulk material is bombarded with the neutron radiation, different characteristic gamma-ray energy spectra are produced from different elements in the bulk material. By processing detected signals indicative of gamma ray energies, a measurement can be made regarding the elemental content of the bulk material. Directing a PGNAA analyzer at a stream of industrial material can allow the full stream to be analyzed and an accurate assessment of the composition of bulk materials can be provided quickly, without special processing of the materials. For further details regarding PGNAA analyzer, see U.S. Pat. Nos. 7,152,002 and 7,778,783, which describe improvements for substance analyzers using Prompt Gamma Neutron Activation Analysis for identifying characteristics of a substance; these patents are hereby incorporated by reference in their entirety.